Diseases caused by pathologic protein folding are among the most devastating suffered by the aged. These diseases include Alzheimer's, Huntington's, Parkinson's, familial amyloid polyneuropathy, and prion. Each is a fatal disorder causing progressive cognitive and physical decline. Each is linked to aberrant folding of proteins that results in protein dysfunction. Dysfunction comes both from intrinsic changes in protein monomer structure and protein self-association (aggregation). The latter phenomenon occurs frequently in the dementing illnesses, of which Alzheimer's disease (AD) is the most common. In AD, the amyloid beta-protein (Abeta) self-associates to form oligomeric structures that circulate in plasma and cerebrospinal fluid. As the disease progresses, deposits of Aa are found in increasing number and size in the brain. These deposits, termed "amyloid plaques," contain fibrillar polymers of Abeta. Most cases of AD are not linked to mutations in the cognate structural gene for Abeta. This raises the questions of why pathologic folding and assembly of Abeta occur and why disease incidence increases so sharply after the age of 65. AD is not unique in these respects, as other dementing illnesses also are "diseases of aging." The general problem area addressed by this Program Project (Program) is pathologic protein folding and assembly, as exemplified by Abeta. We hypothesize that conformational changes in Abeta lead to oligomerization and that the resulting oligomeric assemblies are the proximate neurotoxins causing AD. To test this hypothesis, we propose two long-term specific aims: 1. To understand, at the most fundamental biophysical and cellular levels, how aberrant folding of proteins produces human disease. 2. To translate this knowledge into the design and implementation of new therapeutic agents. To accomplish these aims, five principal investigators at four different American universities have joined together to create a tightly-integrated program comprising two administrative cores and five projects. Our long-term strategy seeks first to establish a cohesive and productive research enterprise focused on AD and Abeta. We make this choice because AD is the most common cause of late-life dementia, its incidence is predicted to increase significantly, and Abeta assembly has proven to be archetypal for amyloid proteins. This last point is important, because the Program is designed to advance our understanding of AD and provide new technologies applicable in studies of folding and assembly of other amyloid and non-amyloid proteins. We thus envision the significance of the Program extending beyond solely AD.